1. Field of the Invention
The present invention relates to navigation equipped device-land vehicles, preferably driverless. More particularly, this invention pertains to a sensor fitted to such a vehicle that serves to detect lateral drive (i.e. movements transverse to the longitudinal axis of the vehicle) to permit a track correction when the vehicle deviates from a predefined path.
2. Description of the Prior Art
Driverless land vehicles, in particular transport vehicles or industrial trucks, are used to an increasing extent in warehouses, assembly halls and the like for path-specific transport and positionally accurate parts delivery. Such vehicles assume diverse designs. These are described, by way of example and preferably in conjunction with transport systems, in the following patent publications: EP-B1-0 391 206; U.S. Pat. Nos. 4,908,557; 4,772,832; EP-B1-0 278 853; DE-U1-87 01 762; DE-A-1 802 793; and DE-A1-36 06 418.
It is known to equip such driverless land vehicles with a navigation system, preferably one based on a fiber-optic gyroscope. To increase the tracking accuracy of such transport vehicles, particularly significant, for example, for positionally accurate charging of production lines, it is known, inter alia, from the above documents, to set track correction points, preferably in the form of permanent magnets, into the floor or the roadway covering, along a predefined route. At these correction points, the track predefined by the navigation device is checked and, if necessary, corrected and updated.
Although such transport systems operate satisfactorily in many applications, improvements in tracking accuracy are desirable. As a rule, the driving wheels of driverless transport vehicles are covered with hard natural rubber. The surface (i.e., the roadway covering) on which the transport vehicle moves is not always sufficiently even to prevent non-negligible transverse forces from arising. In addition, roadway coverings change during the course of use and/or as a result of the loading or transshipment of large masses, such as machines. Such transverse forces can then cause a lateral drift as the natural rubber covering of the wheels is not infinitely rigid. Furthermore, non-negligible transverse forces are produced when traveling through curves. Their effects have also been observed to be non-negligible during test runs. As a result of such transverse forces, it is not possible to carry out angle corrections using known navigation algorithms, shortly after traveling through a curve.